Bonding Situation in Stannocene and Plumbocene N-Heterocyclic Carbene Complexes

Abstract

A detailed experimental and computational study of a series of stannocene and plumbocene N-heterocyclic carbene complexes is presented. This unique class of group 14 Lewis acid−base adducts was obtained from reactions of the corresponding metallocenes and Nheterocyclic carbenes (NHC) and was structurally characterized by single-crystal X-ray diffraction. The obtained structures show a perpendicular pose of the NHC with respect to the metallocene, hence precluding the maximum interaction between the moieties. The nature of the Sn−CNHC and Pb−CNHC bonds has been investigated by applying natural bond orbital (NBO) analysis and energy decomposition analysis (EDA-NOCV). For the sake of comparison, known stannocene and plumbocene Lewis base complexes have been included in the series. The attractive chemical bonding interactions are around 50% electrostatic, 30% covalent, and 20% dispersion. Indeed, dispersion interactions play a determining role the larger the substituents become. The covalent interactions derive from the donation of the carbene ligand into the empty p orbital of the metallocene.